Exposure control device for a camera

ABSTRACT

An exposure control device for a camera comprising; first means for measuring light from a central area of an object field, said first measuring means including a plurality of means for receiving light from different portions within the central area, respectively; second means for measuring light from a surrounding area other than the central area, the surrounding area being greater than each portion within the central area; means for selecting between a first exposure control mode and a second exposure control mode; and means for controlling exposure in accordance with one of said plurality of receiving means in said first exposure control mode, and in accordance with all of said plurality of receiving means and said second measuring means in said second exposure control mode.

This application is a continuation, of application Ser. No. 905,267,filed Sept. 9, 1986 now U.S. Pat. No. 4,821,074 4/11/89.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exposure control device for acamera, and more particularly to such a device capable of measuringlight from different areas of an object field for controlling anexposure.

2. Description of the Prior Art

In the field of art various types of the above mentioned device havebeen provided, such as disclosed in U.S. Pat. No. 4,514,073 and Japaneselaid open Patent Application No. 59-123824.

In U.S. Pat. No. 4,514,073, there is shown a device capable of selectingbetween a spot metering mode and an averaged metering mode. In Japaneselaid open Patent Application No. 59-123824, there is disclosed anexposure control device which includes a first means for measuring lightfrom a central area of an object field, a second means for receivinglight from a surrounding area other than the central area, and means forcontrolling exposure in accordance with the first receiving means in afirst mode, and in accordance with the first and second receiving meansin a second mode. The location of the central area in the object field,however, is not variable, but is fixed with respect to the field ofview.

On the other hand, there is disclosed, in Japanese laid open UtilityModel Application No. 53-148638, a camera including means for adjustingthe focus of the camera with respect to a limited area of an objectfield and means for controlling the exposure by means of measuring lightfrom an area substantially the same as the limited area. This is forrealizing a correct exposure for the limited area of the most interestwhich is subject to the automatic focus adjustment. However, a correctexposure determined with only the limited area taken into considerationwould not always be a correct exposure for an entire object field.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved exposurecontrol device capable of measuring different areas of an object field.

Another object of the present invention is to provide an exposurecontrol device capable of measuring light from a limited area and alsofrom a greater area including the limited area, wherein the limited areais variable within the greater area.

Still another object of the present invention is to provide an exposurecontrol device in which an exposure for a limited area of the mostinterest which is subjected to the automatic focus adjustment isautomatically corrected in case of necessity by means of measuring lightfrom an area other than the limited area.

According to the feature of the present invention, the exposure controldevice comprises

first means for measuring light from a central area of an object field,said first measuring means including a plurality of means for receivinglight from different portions within the central area, respectively;

second means for measuring light from a surrounding area other than thecentral area, the surrounding area being greater than each portionwithin the central area;

means for selecting between a first exposure control mode and a secondexposure control mode; and

means for controlling exposure in accordance with one of said pluralityof receiving means in said first exposure control mode, and inaccordance with all of said plurality of receiving means and said secondmeasuring means in said second exposure control mode.

According to another feature of the present invention, the exposurecontrol device comprises

first means for measuring light from a first area of an object field;

second means for measuring light from a second area of an object fieldother than the first area;

means for detecting focus to at least a position within said first area;

means for adjusting focus in response to said detecting means togenerate an in-focus signal when an in-focus condition is established;

means for modifying a light measuring output from said first measuringmeans with a light measuring output from said second measuring means togenerate a third light measuring signal;

means responsive to said first and second measuring means for examiningwhether or not an exposure control in accordance with only said firstmeasuring means is appropriate; and

means for controlling exposure in accordance with the light measuringoutput from said first measuring means obtained upon the generation ofthe in-focus signal when said examining means decides appropriate, andin accordance with the third light measuring signal obtained upon thegeneration of the in-focus signal when said examining means decidesinappropriate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1b are respectively schematic diagrams showing an opticalsystem of a camera to which an exposure control device according to thepresent invention is applied,

FIG. 2 is an enlarged front view of a light measurement unit used in theembodiment shown in FIG. 1A,

FIGS. 3A and 3B are respectively schematic diagrams showing a front viewof a finder used in the camera shown in FIG. 1 with the operation of thelight measurement shown,

FIG. 4 is a circuit diagram showing an example of the exposure controldevice according to the present invention,

FIG. 5 is a time chart showing an operation of an automatic focusingcontrol device shown in FIG. 4,

FIG. 6 is a schematic diagram showing various operation modes in theexposure control device according to the present invention,

FIG. 7 is a graph showing a way of correction of the light measurementvalue according to the present invention,

FIG. 8 is a schematic diagram showing an example of display used in theexposure control device according to the present invention, and

FIG. 9 comprised of FIG. 9A to FIG. 9D to FIG. 15 are respectively flowcharts showing the operation of the exposure control device according tothe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1A and 1B there is shown an example of an opticalsystem of a divided light measuring device according to the presentinvention. FIG. 1A shows a condition before and after exposure and FIG.1B shows a condition during exposure.

There is disposed a half mirror MR1 which is rotatably supported at oneend thereof behind an objective lens LE1. Normally the half mirror MR1is positioned in the slanted attitude as shown in FIG. 1A. Disposedbehind the half mirror MR1 are a shutter SH which can be released at thetime of picture taking and a photographic film FLM. A pentagonal prismPL is disposed above the half mirror MR1 and a light measuring block FIis disposed behind the prism PL. The light measuring block FI includes ahalf mirror MR2, a light measuring device SPCA for measuring naturallight and a lens LE2, the light projected from the prism PL entering inthe half mirror MR2 to be further projected to the light measuringdevice SPCA through a lens LE2. A sub mirror SM is further disposedbehind the half mirror MR1 so as to project the light from the halfmirror MR1 to an image sensor CCD made of CCD array for an automaticfocusing control. Both half mirrors MR1 and MR2 can rotate togetherbetween positions in FIGS. 1A and 1B. When the half mirror MR1 is in theclosed position as shown in FIG. 1A, the light from the objective lensLE1 is reflected partly to the prism PL and partly passed through to theimage sensor CCD by way of the reflection at the sub mirror SM. On theother hand, when picture taking, the half mirror MR1 and sub mirror SMcan be retracted as shown in FIG. 1B so as to pass the entire light fromthe lens LE1 to the photographic film FLM. In order to receive the lightreflected from the photographic film FLM, there is provided a lightreceiving element SPCB for the purpose of flash light control. AFMrepresent a motor to drive the objective lens LE1 for an automatic focuscontrol.

The arrangement of the light measuring device SPCA is shown in FIG. 2,wherein a pair of photo sensors SPC1 and SPC2 are juxtaposed in thecentral area of the device SPCA for measuring the intensity of lightincident to the central portion thereof and another photo sensor SPC3for measuring the intensity of light incident to the peripheral portionof the device SPCA. It is noted that FIG. 2 is depicted in a shapeviewed from the finder in which a mark AFZ is displayed for clearlyshowing an automatic focus zone.

FIGS. 3A and 3B are for considering a divisional light measurementperformed by the photo sensor SPC1 or SPC2 which includes the automaticfocus zone AFZ, in which an automatic exposure is carried out inrelation with the automatic focus adjustment. Assuming to take a pictureof human's portrait including the face and the body wearing a cloth, ifthe face is situated in the automatic focus zone AFZ as in FIG. 3A,light measurement for the face can be made correctly by means of SPC2.However, if the body is situated in the automatic focus zone AFZ, asshown in FIG. 3B, a light measurement by SPC2 would cause over exposureor under exposure for the face depending on the reflection factor of thecloth. In order to eliminate the problem mentioned above, two photosensors SPC1 and SPC2 are provided in accordance with the presentinvention and the exposure value is decided by the output of any one ofthe photo sensors SPC1 or SPC2 which actually receives smaller light.That is, as shown in FIG. 3A, in case the photo sensor SPC2 measures thelight of the human's face and the photo sensor SPC1 measures back groundwhich is brighter than the face, the output of the photo sensor SPC2which receives the smaller value of light is selected so that a correctexposure for the face is realized. On the other hand, as shown in FIG.3B, assuming that the photo sensor SPC1 measures the human's face andthe photo sensor SPC2 measures the human's cloth, in case the cloth iswhitish and the reflection factor of the cloth is greater than thereflection factor of the face, the output of the photo sensor SPC1 whichreceives smaller amount of light is selected so that a correct exposurefor the face is realized. In case of FIG. 3B, if the cloth is dark andthe reflection factor of the cloth is less than the reflection factor ofthe face, the output of the photo sensor SPC2 would be selected and theexposure value is decided for the dark cloth, which would cause an overexposure amount is over exposure for the human's face. However since thephotographic film has a wide latitude against the over exposure, it ispossible to take a good picture without any problems in such a case.

As will be understood from FIG. 8, a display unit LCD is furthervisually provided in a suitable portion of finder view field accordingto the present invention. The display unit LCD comprises a mark 10showing a day light synchro mode, a mark 11 showing a flash light mode,marks 12 and 13 showing average light measurement and spot lightmeasurement and a digital display unit 14. The respective marks anddigital display unit are made of for example LCD (liquid crystal displaydevice).

A circuit arrangement for the exposure control device according to thepresent invention is explained with reference to FIG. 4 in which acentral processing unit (referred to as CPU hereinafter) made of amicroprocessor is represented by CPU. E denotes a battery to which acapacitor C1 and a resistor R1 are connected to form a power on resetcircuit for generation of a signal for resetting the CPU at the time ofmounting the battery E. A transistor Tr acts to provide power source Vccto peripheral circuits. Connected to CPU are first switch SW1 which isturned on in response to an initial step of press of a release button(not shown) of the camera up to the first depth, for executing the lightmeasurement and automatic focus and second switch SW2 which is turnedon, in response to an advanced step of press of the release button up tothe second depth which is deeper than the first depth, for triggeringthe shutter release. The information of a fully opened aperture valueAVo and the minimum aperture value AVmax are respectively fed from thelens circuit attached in the lens LE1. Sv represents a set film speedinformation. Mg1 denotes a release magnet for executing release of theshutter. Mg2 denotes a front curtain magnet, Mg3 a rear curtain magnetand Mg4 a control magnet. The outputs of the photo sensors SPC1 to SPC3are respectively selected by switches Swc1 to Swc3 and the selectedsignal is logarithmically compressed in the logarithmic compressingcircuit composed of an operation amplifier OP1 and compression diodeDd1, then fed to a further operation amplifier OP2 for level shiftingand converted from the analog signal to the digital signal in a A/Dconverter ADC and in turn the digital signals are applied to CPU. Apulse generator FP applies pulse signals in the course of stopping-downoperation of the aperture from its full open size, the number of pulsesbeing counted by CPU for monitoring the advance of stopping-downoperation. A switch controller SWC acts to change over the switches Swc1to Swc3 in response to the instructions fed from CPU.

The output of the photo sensor SPCB measuring the light reflected fromthe photographic film FLM is applied to one input terminal of an adderADD through a logarithmic compression circuit composed of an operationamplifier OP3 and a logarithmic compression diode Dd2. Another inputterminal of the adder ADD is applied with a signal from CPU through aD/A converter DAC. The signal added in the adder ADD is integrated in anintegral circuit INTE and the integrated signal is compared in acomparator C with a reference signal Vref. When the integrated signalexceeds the reference signal Vref, the comparator C gives a signal to aflash device FL so as to order to turn off the flash light. Integrationin the integration circuit INTO can be initiated by an AND signal fedfrom an AND gate AN1 which receives a signal INTS from CPU and a signalat a contact (b) which is generated in response to change over of the Xcontact SWX for triggering the flash device FL toward (a) side from (b)side.

The image of the photographic object situated in the automatic focuszone AFZ at the central portion of the finder can be sensed by the imagesensor CCD and the sensed signal is fed to an automatic focus controlcircuit AFC through an interface IF. In the automatic focus controlcircuit AFC, the auto-focusing motor AFM is driven by the auto-focusingstart signal AFS fed from CPU so as to shift the lens LE1 along theoptical axis for focusing. When automatic focusing with respect to thephotographic object taken in the automatic focus zone AFZ is oncecompleted, the auto-focusing motor AFM is stopped and a signal AFE(referred to as focus completion signal hereinafter) representingcompletion of the automatic focusing is applied to CPU.

As in the above, the embodiment carries out the so-called "one shotautomatic focus adjustment". FIG. 5 shows the time chart of theoperation thereof. In the time chart, "0" level for the switch SW1 andauto-focusing start signal AFS represent that the switch SW1 is ON andthe signal AFS is generated respectively. On the other hand, "1" levelfor auto-focusing completion signal (AFE) represents that the automaticfocus adjustment has once been completed. In case the switch SW1 is keptON after completion of the auto-focusing, the lens LE1 is locked in thein-focus position and the auto-focus controller AFC computes only thedistance measurement and the result of the distance measurement isapplied to CPU through the line P1. In order to start the automaticfocus control again, it is necessary to turn off the switch SW1 oncethen to turn on it again. When the switch SW1 is in OFF state, theauto-focusing start signal AFS is made 1 and the focus completion signalAFE is made 0 so that the operation returns to the initial state.

In CPU, INT1 and INT2 represent ports for receiving interruption.

Operation of the exposure control device is explained hereinafter by theaid of flow chart in FIGS. 9 to 15.

When the battery E is mounted in the camera in position, the power onreset is effected as shown in FIG. 10, wherein the respective outputports of CPU are initialized in the step S10 and the flag AFEF is set to"0" in the step S11. The "0" state of the flag AFEF means that thepresent state is not immediately after the automatic focus completion.In the step S12 an interruption to the port INT2 is disabled. In thestep S13 the interruption to the port INT1 is enabled, then CPU is putin the stand-by condition in the step S14 and CPU stops untilinterruption is ordered. When the switch SW1 is turned on by pressing ofthe release button up to the first depth, the signal is applied to theport INT1 to effect the INT1 interruption and the processes shown inFIG. 9 is started.

In the step S20, the signal PWC is made 0 to turn on the transistor Trto supply the power source to the peripheral circuits. Subsequently thecontent of the display unit LCD is cleared in the step S21. In the stepS22, the condition of the switch SW1 is detected and if the switch isON, the signal AFS is made 0 in the step S23 so as to enable theautomatic focus controller AFC to carry out the automatic focusingoperation. On the other hand, if the switch SW1 is OFF, AFEF=0 is set inCPU in the step S24 to represent that the present state is notimmediately after the auto-focusing completion. Then the step goes toS25 to make the signal AFS=1, thereby stopping the automatic focusingoperation. In this embodiment, CPU keeps its operating condition for apredetermined time even after the switch SW1 is turned off. Step S25 isfor preventing the automatic focusing operation after the switch SW1 ismade OFF.

In the step S26, it is judged whether or not the signal AFE=1 fordetecting whether or not the auto-focusing is completed. In case thesignal AFE is 0 which means that the auto-focusing is not completed, thestep goes to S29, on the other hand, with AFE=1, the step goes to S27 tojudge whether or not the present state is immediately after thecompletion of the auto-focusing by the state of the flag AFEF. If AFEFis 1 at the step S27, the step goes to S30, on the other hand, withAFEF=0, the flag AFEF is set to 1 in the step S28, then goes to the stepS29. The step S29 comprises a subroutine for taking the lightmeasurement value Bv in CPU. By this operation, the light measurementvalue Bv is continuously taken in CPU until completion of theauto-focusing, however, after completion of the auto-focusing, the lastlight measurement value immediately after the completion of theauto-focusing is stored in a memory but the light measuring valuethereafter is not taken in CPU. However, if the depression of therelease button is ceased and the switch SW1 is turned off, therefore thesignal AFEF becomes 0, the light measurement value can be taken in CPUagain. The subroutine of the step S29 is shown in FIG. 11 in detail.

The value n is set to 1 in the step S291 of FIG. 11 and a value n-1 isrepresented by the combination of the signals SWCC1 and SWCC2 on theterminals P4 in the step S292. The switch controller SWC is controlledin response to the value n-1 for turning on any one of the switches SWC1to SWC3 to select any one of the photo sensors SPC1 to SPC3 inaccordance with the following Table 1:

                  TABLE 1                                                         ______________________________________                                        n   SWCC1      SWCC2    SWC1    SWC2  SWC3                                    ______________________________________                                        0   0          0        a       b     b                                       1   0          1        b       a     b                                       2   1          0        b       b     a                                       3   1          1        a       a     a                                       ______________________________________                                    

As will be understood from the Table 1, the location of spot measuringarea can be shiftable between two cases where n-1=0 (SPC1) and n-1=1(SPC2), and a light measurement by all the photo sensors(SPC1+SPC2+SPC3) is also possible where n-1=3.

A signal ADSTR for starting the A/D converter ADC is made 1 in the stepS293 and the output of the selected photo sensor or photo sensors (anyone of SPC1 to SPC3) is converted from the analog signal to the digitalsignal and is applied to the terminal P₀ of CPU. Then the step goes toS294 wherein it is judged whether or not the A/D conversion is completedby judging 1 of the signal ADE from the A/D converter ADC. With thecompletion of the A/D conversion, the step goes to S295, wherein thesignal on the terminal P₀ is taken in CPU and stored in the registerBVn. (in this case BV1). The value n is updated to increase by 1 in thestep S296. Then the step goes to S297, wherein it is detected whetherthe value n<4. Namely the processes S292 to S296 are repeated until thevalue n becomes 4. Accordingly, the values of the output of the photosensors SPC1, SPC2, SPC3 and SPC1+SPC2+SPC3 are respectively stored inthe registers BV1 to BV4. The values stored in the registers BV3 and BV4are corrected in the steps S298 and S299 by correcting the outputdifference of the respective light receiving area of the photo sensorsSPC1 to SPC3 and SPC1+SPC2+SPC3. For example, assuming that the ratio ofthe light receiving areas of the photo sensors SPC1 and SPC3 is 1:8, theoutput of the photo sensor SPC3 is decreased by 3 Ev steps. Furthermore,assuming that the ratio of the light receiving areas of the photosensors SPC1 and SPC1+SPC2+SPC3 is 1:10, the total output ofSPC1+SPC2+SPC3 is decreased by 3.3 Ev steps.

Referring to FIG. 9, again, the aperture values AV_(O), AV_(max) andfilm speed SV are taken in CPU in the steps S30 to S32. Then in the stepS33, the charge completion signal RDY from the flash device FL isjudged. In case the charge to main capacitor in the flash device iscompleted and the signal RDY is 1, the step goes to after S60 for theflash operation mode, to the contrary, if the charge is not completed,and the signal RDY is 0, the step goes to after S34 for the ambientlight operation.

In the steps S34 to S36, one of the outputs of the photo sensors SPC1and SPC2 which receives less light is selected out as the value BVa,then it is judged in the steps S37 whether or not the selected value BVais greater than the predetermined value E. If the value BVa is smallerthan the value E, BVa is further compared with D in the step S38, and anaverage light measurement value BV4 is adopted as the light measurementvalue at the step S39 if BVa<D.

As mentioned above, in the present embodiment,

(a) In case the light measurement value at the central portion of thelight measuring device SPCA is smaller than the predetermined value, theaverage light measurement value is used.

(b) In case other than the case (a), the darker light measurement valueof any one of the two photo sensors SPC1 and SPC2 each disposed adjacenteach other in the central portion of the light measuring device SPCA isused.

Therefore, it is possible to eliminate the problem of bad linearity ofthe light measurement value due to such a reason why in case thebrightness of the photographic object is low, the output current of thephoto sensor is low. In addition, by the arrangement mentioned in theitem (b), a correct exposure can be always performed regardless of thereflection coefficient of the photographic object such as human's clothin case the light measuring device SPCA measures the cloth.

In case of D<BVa<E, the light measurement value BVa is compared with thelight measurement value BV3 measured by the photo sensor SPC3 whichsenses the peripheral portion of the light measuring device SPCA in thesteps S40 to S43. In case the brightness difference between BVa and BV3is greater than a predetermined value, the value BVa can be correctedaccording to the difference so as to be an appropriate value in thesteps S44 to S46. Specifically, in case of 1<BVa-BV3<3, the value BVa iscorrected according to the equation BVa=BVa+1/2 (BV3-BVa-1) in the stepS45. In case of BVa-BV3<3, the value BVa is corrected according to theequation BVa=BVa-1 for BV3<BVa or BVa=BVa+1 for BV3<BVa in the steps S46or S44, respectively. By the correction mentioned above, it is possibleto prevent making such a bad picture that the sub photographic objectsuch as background or the like becomes white in case a correct exposureis conducted for only the main object under a large brightnessdifference between the main object and sub object due to rear lightpicture taking.

FIG. 6 shows the change of the light measuring mode corresponding to thechange of light measurement value BV (which is BV1 or BV2) and BVa-BV3.FIG. 7 shows the correction of the value BVa corresponding to thedifference BVa-BV3.

The light measurement value BVa thus obtained as mentioned above isadded by the film speed SV for obtaining an exposure value Ev in thestep S47. The maximum exposure value EV_(max) is calculated in the stepS48 corresponding to the shortest shutter time TV₁₀ and minimum aperturesize value AV_(max). Subsequently, the necessary shutter time TV andaperture value AV are calculated in the steps S49 and S50 according tothe following equations.

    TV=TV.sub.10 -1/2(EV.sub.max -EV)

    AV=AV.sub.max -1/2(EV.sub.max -EV)

It is judged in the step S51 whether the calculated aperture value Av issmaller than the aperture diameter of the full opened aperture valueAV_(O). With AV<AV_(O), the shutter time TV and the aperture value AVare changed in the steps S52 and S53 according to the equations

    TV=EV-AV.sub.O

    AV=AV.sub.O.

On the other hand, if AV>AV_(O), the calculated TV and AV aremaintained.

Referring to FIG. 12 showing the details of the sub routine for displayI at the step S54 of FIG. 9C, the mark 10 in FIG. 8 showing the daylight picture taking mode and the mark 11 also in FIG. 8 showing theflash picture taking mode are respectively deleted in the step S541. Inthe step S542, BVa<D is judged. In case BVa<D that is the lightmeasurement value at the center of the light measuring device SPCA issmaller than a predetemined value D, the display showing the averagelight measurement exposure is displayed in the display device LCD ofFIG. 8 using elements 12 and 13 in the step S543. In one example, theaverage light measurement exposure can be represented by making bothelements 12 and 13 so that the square mark is made dark as a whole. Incase the light measurement value BVa is greater than the predeterminedvalue D, the brightness of the peripheral portion of the light measuringdevice SPCA and the light measurement value BVa are compared in the stepS544 and if the brightness difference is smaller than a value K, a darkmark is displayed in the circular portion 13 of the display device LCDfor displaying the spot light measurement exposure in the step S545. Incase the brightness difference between the light measurement value BVaand the brightness of the peripheral portion of the light measuringdevice SPCA is greater than the predetermined value K, a mark showingthe rear light light measurement exposure is displayed in the step S546.In the example, the rear light measurement exposure is displayed byturning on and off alternatingly the element 12 with element 13unchanged. By the arrangement mentioned above, an operator can know whatexposure mode is used directly and there is no need to provide aseparated light measuring device for detecting the rear light condition.Subsequently the shutter time TV and aperture value Av are displayed inthe four digit display area 14 in the step S547. When the above routinecorresponding to the step S54 in FIG. 9C is completed, the step goes toS80 of FIG. 9D.

In case it is detected in the step S33 of FIG. 9A that the charging ofthe main capacitor of the flash device is completed, the program for theflash picture taking after the steps S60 of FIG. 9B is performed. It isdetected in the step S60 whether the difference between the value BV3showing the brightness in the peripheral portion and the value BV1 ofthe central portion is not greater than 3. Also whether or not thedifference between the value BV3 and the central portion BV2 is notgreater than 3 is detected in the step S61. If both of the differencesare not greater than 3, the light measurement value BV3 is used as thelight measurement value BVf in the step S62.

In case the difference is greater than 3 in the step S60 (or S61), thatis in case of the rear light picture taking mode, the value BVfcalculated by the following equation

    BVf=BV3-1/3(BV3-BV1 (or BV2))

is used as the light measurement value BVf for the flash light picturetaking in the step S63 (or S66). In other words, the valued BVf can beobtained by modifying BV3 in accordance with the difference between thevalue BV3 of the peripheral portion and the values BV1 or BV2 of thecentral portions of the light measuring device SPCA. It is judged in thestep S64 (or S67) whether or not the value BVf obtained in the step S63(or S66) is less than BV3-3. When BVf is less than BV3-3, the value BVfis determined by BV3-3 in the step S65 (or S68) in place of thedetermination of BVf in the step S63 (or S66). When BVf is greater thanBV3-3, on the other hand, the value BVf obtained in the step S63 (orS66) is maintained as it is. Thus the modification of the value BVfthrough steps S63 to S68 is limited to a shift by value 3 in any case.Namely,

(a) in case the peripheral portion of the light measuring device SPCA isremarkably brighter than the central portion thereof, an over exposure(less than 3 Ev) is set for the peripheral portion. The central portionwhich may be under exposure is compensated by the flash light.

(b) in case there is few difference in brightness between the centralportion and peripheral portion of the light measuring device SPCA, anappropriate exposure value is employed for the peripheral portion. Theexposure for the central portion is controlled by the flash light.

By the arrangement mentioned above, in case of rear light picturetaking, the peripheral portion may be over exposed so that a picturewith a natural rear light effect can be realized as viewed by eyes.

Subsequently, the light measurement value BVf is added with the filmspeed SV for obtaining the exposure value EV in the step S69, then inturn the aperture value AV appropriated for the synchronized shutterspeed TVx in the step S70. It is judged in the steps S71 and S72 whetherthe calculated aperture value AV is greater than the minumum aperturesize value AVmax or less than the full open aperture value AV₀. In casethe aperture value AV is out of the range from AV₀ to AVmax, the minimumaperture size value AVmax or full open aperture value AV₀ is used in thestep S73 or S74 and the step goes to S75 of the display II routine asshown in FIG. 13.

The display II relates to the charge completion of the flash device andthe day light flash photography. In the step S751, the mark 11 shown inFIG. 8 is turned on. In the step S752, the marks 12 and 13 are turnedoff. In the step S753, the shutter speed TV and aperture value AV aredisplayed at the display unit 14. The value BVf when the flash light isused is compared with 3 in the step S754. In case BVf is greater than 3,the mark 10 for the day light synchro (i.e., day light flashphotography) is turned on in the step S755. In case BVf is smaller than3, on the other hand, the step goes to S756 to turn off the mark 10.When the display II routine is completed, the step goes to S80 in FIG.9D to judge whether or not the flag AFEF is 1 in which the state isimmediately after the auto-focusing is completed.

In case the flag AFEF is 0 that is the auto-focusing is not completed,the step goes to S81 to make the defocus value (DEF) 0. The term ofdefocus value shows the displacement of the image formed by the lensfrom the focal plane. In case the flag AFEF is 1, although the lens LE1is not driven, the auto-focus controller AFC is enabled so that thedefocus value DEF is applied consecutively to CPU from the auto-focuscontroller AFC through the terminal P1. The defocus value DEF obtainedin the step S82 is utilized for adjusting the flash light value asmentioned hereinafter. In the step S83, the signal INT1 is judged todetect whether or not the switch SW1 of the release button is made ON.In case the switch SW1 is on, the timer in CPU is stopped in the stepS84 and present in the step S85. In case the switch SW1 is off, the stepgoes to S86 to start the timer in CPU so as to supply the power for thepredetermined time even if the switch SW1 is turned off with the releasethe button unpressed. In case the switch SW1 is not turned on againduring the predetermined time set by the timer, the step returns to S10by the timer interruption to bring CPU at the stand-by condition. In thestep S87, it is judged whether or not the switch SW4 which is tuned offby the completion of the film winding by one frame. In case the switchSW4 is OFF, the interruption to the port INT2 is enabled in the step S88to go to the step S22 in FIG. 9A. In case the switch SW2 is turned on bythe press of the release button up to the second depth, the INT2interruption is triggered and the INT2 routine shown in FIG. 14 isperformed.

Referring to FIG. 14, the INT2 interruption is disabled in the step S100and the magnets Mg2, Mg3 for the first and second curtains and theaperture control magnet Mg4 are turned on in the steps S101, S102 andS103. These operations are caused by the signals 1CMg, 2CMg and FMg turnto "1", respectively.

In the step S104, the flash light value DASV is set by the film speedSV, then the value DASV is corrected corresponding to the defocus valueDEF in the steps S105 to S108. Specifically, it is judged whether or notthe value DEF is greater than a predetermined value d in the step S105.In case DEF is greater than d that is in case the photographic object inthe center of the finder at the time of the shutter releasing is locatedfurther from the camera than the distance at the time of the focuslocking, 1 is added to the value DASV. To the contrary, in case thevalue DEF is smaller than -d, that is the photographic object in thecenter of the finder is located closer to the camera, the value DASV issubtracted by 1.

Thus, the flash light value is controlled according to the defocus valuein a manner summarized below.

(a) In case of -d<DEF<d, normal flash light value which provides acorrect exposure for an object at the center of the object field isused.

(b) In case of DEF<d, the flash light is slightly reduced than tha case(a).

(c) In case of DEF<-d, the flash light is slightly increased than thecase (a).

In the flash device of a TTL (through the lens) light adjustment type,when there is not the photographic object in the central portion of thefinder but is located in the peripheral portion thereof with abackground located in the central portion, an over exposure tends tooccur corresponding to the light measurement map since the reflectionfrom the central portion of the finder is few. To the contrary, in casethe sub object located in the central portion is located nearer to thecamera than the main object located in the peripheral portion, an underexposure tends to occur. These phenomena may occur when the flash deviceis controlled by receiving reflection light which does not pass throughthe objective leans is used due to the light measurement map and theuneven light distribution.

However, by correcting the amount of the flash light as mentioned above,even if the main object which was in the central portion of the viewfinder upon automatic focus adjustment is arrnged out of the centralportion of the picture at the time of shutter releasing, the main objectcan be exposed with the appropriate exposure value irrespective of thedistance of the sub object situated in the central portion of thepicture. The correction mentioned above may be changed depending on thevalue d.

Referring to FIG. 14 again, the light value DASV is supplied from CPU tothe D/A converter DAC through the port p3 in the step S109 and isconverted into the analog form. Then the signal AFS is made 1 to stopthe function of autofocus controller AFC in the step S110. Subsequentlythe signal ADSTR is made 0 in the step S111 to stop the A/D converterADC. The the signal RMg is made 1 in the step S112 and the releasemagnet Mg1 is excited to release the shutter. After waiting for 5 msec.in the step S113, the signal RMg is made 0 to deenergize the releasemagnet Mg1 in the step S114. The number of step AVr for controlling theaperture value from AVO to AV is calculated in the step S115, and thenumber of step AVr is stored in the event counter in CPU in the stepS116, then the event counter starts in the step S117. By the way, whenthe release magnet Mg1 is excited to release the aperture closingelement which is initially situated at the fully opened position, theaperture closing element is moved toward the closing position. Duringthe stopping-down motion of the diaphragm aperture, the pulses fed fromthe pulse output circuit FP corresponding to the movement of theaperture closing element are counted by the event counter. When thenumber of pulses corresponding to the step AVr of the aperture closingvalue preset in the event counter are counted, an interruption isapplied by the event counter. In FIG. 15 in which the routine caused bythe event counter interruption is shown, the siganl FMg is made 0 in thestep S1181 to turn off the magnet Mg4, whereby the movement of theaperture closing element is stopped and the diaphragm aperture is set inposition corresponding to the aperture value AV. In FIG. 14, subsequentto the step S117, the program waits for 50 msec. in the step S119.Thereafter, the signal INTS is made 1 in the step S120 so as to enablethe AND gate AN for preparing the start of integration circuit INTEwhich is to be caused by the switch SWX changed over to the position(a). The signal 1CMg is made 0 in the step S121 to deenergize the magnetMg2 for moving the first curtain. In the step S122 the shutter open timeSS is counted and when a predetermined time is reached, the signal 2CMgis made 0 in the step S123 to turn off the magnet Mg3 so that the secondcurtain is moved to close the shutter and the exposure is finished. Whenthe switch SW4 which has been set in the off state by the completion ofthe film winding is detectd in the step S124 to be turned on by thecompletion of the movement of the second curtain, the step goes to S125for waiting 50 msec. After waiting 50 msec., the signal INTS is made 0and the operation returns to the INT1 routine in FIG. 9A.

Although there are provided two photo sensors SPC1 and SPC2 in thecentral portion of the light measuring device SPCA, only one photosensor may be used in the central portion if limited operations which donot necessarily need two photo sensors are only desired.

It is noted that the present invention may be applied to a camera systemusing a camera and a flash device which controls the flash light amountby itself by measuring light which does not pass through the objectivelens of the camera. In this case the signal representing the defocusvalue occurring at the time of shutter release after an automatic focusis once established and the focus is locked is applied to the flashdevice from the camera, whereby the light adjusting level in the flashdevice is modified in accordance with said signal. Also the presentinvention may be applied to a continuous automatic focusing camera otherthan the one shot automatic focusing camera for a case in which a delayin automatic focus adjustment exists against the change in the object atthe center of the view finder.

It is further noted that there may be provided such a modification whichmerely indicates the rear light condition in place of correcting themeasured light value at the central portion of the light measuring blockat the time of rear light condition under the ambient light. It may bepossible to manually change over between the average light measurementmode and the spot light measurement mode by a change over switch APS (asshown in dotted line in FIG. 4) in place of the automatic change overmeans employed in the embodiment mentioned above.

It is further noted that although in the embodiment mentioned above, thelight value correction is adapted when the absolute value of BVa-BV₃ isgreater than 1 in the steps S44 to S46, it may be possible to correctthe light measurement value only when BV₃ -BVa is greater than 1, whilethe exposure control is performed based on the light measurement valueBVa without correction of the light measurement value when BVa-BV₃ isgreater than 1.

One advantage of the present invention is to enable to take a picturewith a natural rear light effect in day light flash photography by usinga slightly over exposure against the background and using an appropriateexposure by controlling of the flash light to the main object.

Another advantage of the present invention is to enable to control anappropriate exposure by flash light for the main object at theperipheral portion of the object field since the flash light amount ofthe flash light is modified corresponding to the distance information ofthe sub object situated at the central portion of the picture after thefocus is locked at the main object.

A further advantage of the present invention is in that it is capable tochange the location of spot light measurement within the object, e.g.,between human's face and his cloth, without moving the camera.

A still further advantage of the present invention is in that theoperator can know what picture taking mode among the average lightmeasurement mode, partial light measurement mode and rear lightmeasurement mode is going to be performed by the indication on thedisplay device, so that a correct operation can be taken by seeing thedisplay.

A still further advantage of the present invention is to enable to takea picture with a good exposure depicting a natural light contrastpreventing undue brighter portion due to an over exposure even if thepicture is taken under the rear light condition since when it is judgedthat the exposure value by the spot light measurement is not suitable, amodified measurement data is used for deciding the exposure value.

What is claimed is:
 1. A light measuring device comprising:first meansfor measuring light from a central area of an object field; second meansfor measuring light from a surrounding area of the object field; firstmeans for determining whether or not the difference between an output ofsaid first measuring means and an output of said second measuring meansis greater than a first predetermined value; second means fordetermining whether or not said difference is greater than a secondpredetermined value which is greater than the first predetermined value;first means for modifying the output of said first measuring means whenthe difference is greater than the first predetermined value and lessthan the second predetermined value, an amount of the modification beingchanged depending on the difference; and second means for modifying theoutput of said first measuring means by a constant value when thedifference is greater than the second predetermined value.
 2. A lightmeasuring device as claimed in claim 1, further comprising:third meansfor determining whether or not the output of said first measuring meansis less than a third predetermined value; and means for outputting anaverage brightness value depending on the output of both said first andsecond measuring means when the output of said first measuring means isless than the third predetermined value.
 3. A light measuring means asclaimed in claim 1, further comprising:third means for determiningwhether or not the difference is greater than a third predeterminedvalue which is greater than the second predetermined value; and meansfor modifying the output of said first measuring means by a constantvalue when the difference is greater than the third predetermined value.4. A light measuring device comprising:first means for measuring lightfrom a central area of an object field; second means for measuring lightfrom a surrounding area of the object field; first means for determiningwhether or not an output of said first measuring means is less than afirst predetermined value; second means for determining whether or notthe difference between an output of said first measuring means and anoutput of said second measuring means is greater than a secondpredetermined value; and means for calculating brightness data dependingon only the output of said first measuring means when the output of saidfirst measuring means is greater than the first predetermined value andsaid difference is less than the second predetermined value, and forcalculating brightness data depending on both the output of said firstmeasuring means and the output of said second measuring means otherwise.5. A light measuring device as claimed in claim 4, furthercomprising:means for modifying the output of said first measuring meansdepending on the difference when the output of said first measuringmeans is greater than the first predetermined value and said differenceis greater than the second predetermined value.
 6. In a light measuringdevice having first means for measuring light from a central area of anobject field, and means for calculating brightness data depending on anoutput of said first measuring means, the improvement comprising:secondmeans for measuring light from a surrounding area of the object field;first means for determining whether or not the difference between theoutput of said first measuring means and an output of said secondmeasuring means is greater than a first predetermined value; and meansfor modifying the output of said first measuring means when thedifference is greater than the first predetermined value, an amount ofthe modification being changed depending on the difference.
 7. A lightmeasuring device as claimed in claim 6, wherein said modifying meanscomprises second means for determining whether or not the difference isgreater than a second predetermined value which is greater than thefirst predetermined value, and means for modifying the output of saidfirst measuring means by a constant value when the difference is greaterthan the second predetermined value.
 8. A light measuring device asclaimed in claim 6, further comprising:third means for determiningwhether or not the output of said first measuring means is less than athird predetermined value; and means for calculating an averagebrightness data depending on both the output of said first measuringmeans and the output of said second measuring means when the output ofsaid first measuring means is less than the third predetermined value.